Crystalline graphite nanofibers and a process for producing same

ABSTRACT

A carbon nanofiber having substantially graphite sheets that are substantially parallel to the longitudinal axis of the nanofiber and a produce for producing same. The carbon nanofibers are produced by contacting an iron, or an iron:copper bimetallic, or an iron:nickel bimetallic bulk catalyst with a mixture of carbon monoxide and hydrogen at temperatures from about 625° C. to about 725° C. for an effective amount of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. Ser. No.09/659,441 filed Sep. 8, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a process for producing substantiallycrystalline graphitic carbon nanofibers comprised of graphite sheets.The graphite sheets are substantially parallel to the longitudinal axisof the carbon nanofiber. These carbon nanofibers are produced bycontacting a bulk iron, or an iron:copper bimetallic, or an iron:nickelbimetallic catalyst with a mixture of carbon monoxide and hydrogen attemperatures from about 625° C. to about 725° C. for an effective amountof time.

[0004] 2. Description of Related Art

[0005] Nanostructure materials, particularly carbon nanostructurematerials, are quickly gaining importance for various potentialcommercial applications. Such applications include their use to storemolecular hydrogen, to serve as catalyst supports, as reinforcingcomponents for polymeric composites, and for use in various types ofbatteries. Carbon nanostructure materials are generally prepared fromthe decomposition of carbon-containing gases over selected catalyticmetal surfaces at temperatures ranging from about 500° C. to about1,200° C.

[0006] U.S. Pat. Nos. 5,149,584 and 5,618,875 to Baker et al. teachcarbon nanofibers as reinforcing components in polymer reinforcedcomposites. The carbon nanofibers can either be used as is, or as partof a carbon-carbon structure comprised of carbon fibers having carbonnanofibers grown therefrom. The examples in these Patents show thepreparation of various carbon nanostructures by the decomposition of amixture of ethylene and hydrogen in the presence of metal catalysts,such as iron, nickel, a nickel:copper alloy, an iron:copper alloy, etc.

[0007] Also, U.S. Pat. No. 5,413,866 to Baker et al. teaches carbonnanostructures characterized as having a shape that is selected from thegroup consisting of branched, spiral, and helical. These carbonnanostructures are taught as being prepared by depositing a catalystcontaining at least one Group IB metal and at least one other metal, ona suitable refractory support, then subjecting the catalyst-treatedsupport to a carbon-containing gas at a temperature from thedecomposition temperature of the carbon-containing gas to thedeactivation temperature of the catalyst.

[0008] U.S. Pat. No. 5,458,784 also to Baker et al. teaches the use ofthe carbon nanostructures of U.S. Pat. No. 5,413,866 for removingcontaminants from aqueous and gaseous steams; and U.S. Pat. No.5,653,951 to Rodriguez et al. discloses and claims that molecularhydrogen can be stored in layered carbon nanostructure materials havingspecific distances between layers. The examples in these Patents teachthe aforementioned preparation methods, as well as the decomposition ofa mixture of carbon monoxide and hydrogen in the presence of an ironpowder catalyst at 600° C. All of the above referenced US Patents areincorporated herein by reference.

[0009] While various carbon nanostructures and their uses are taught inthe art, there is still a need for improvements before suchnanostructure materials can reach their full commercial and technicalpotential. For example, while the art broadly discloses carbonnanostructures having crystallinities from about 5 to 95%, it hasheretofore not been possible to produce carbon nanostructures withcrystallinities greater than about 95%.

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, there is providedsubstantially crystalline graphitic carbon nanofibers comprised ofgraphite sheets that are substantially parallel to the longitudinal axisof the nanofibers, wherein the distance between the graphite sheets isfrom about 0.335 nm to about 0.67 nm, and having a crystallinity greaterthan about 95%.

[0011] In a preferred embodiment, the distance between the graphitesheets is from about 0.335 and 0.40 nm.

[0012] Also in accordance with the present invention, there is provideda process for producing substantially crystalline graphitic carbonnanofibers which process comprises reacting a mixture of CO/H₂ in thepresence of a bulk powder catalyst comprised of iron, iron:copperbimetallic, or iron:nickel bimetallic for an effective amount of time ata temperature from about 625° C. to about 725° C.

[0013] In a preferred embodiment, the catalyst is an iron:copperbimetallic catalyst wherein the ratio of iron to copper is from about1:99 to about 99:1 and the ratio of CO to H₂ is from about 95:5 to about5:95, preferably from about 80:20 to about 20:80.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1a is a representation of a platelet carbon nanofiber, whichis comprised of substantially graphite sheets that are substantiallyperpendicular to the longitudinal axis, or growth axis, of thenanofiber.

[0015]FIG. 1b is a representation of a cylindrical carbon nanostructurethat is comprised of continuous carbon sheets and is in the form of tubewithin a tube within a tube and having a substantially hollow center.

[0016]FIG. 1c is a representation of a ribbon carbon nanofiber of thepresent invention that is comprised of graphitic sheets that aresubstantially parallel to the longitudinal axis of the nanofiber.

[0017]FIG. 1d is a representation of a faceted tubular carbon nanofiberof the present invention and is comprised of continuous sheets ofgraphic carbon but having multifaceted flat faces. The graphitic sheetsare also substantially parallel to the longitudinal axis of thenanofiber.

[0018]FIG. 1e is a representation of a herringbone carbon nanofiberwherein the graphitic platelets or sheets are at an angle to thelongitudinal axis of the nanofiber.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The carbon nanofibers of the present invention possess novelstructures in which graphite sheets, constituting the nanostructure, arealigned in a direction that is substantially parallel to the growth axis(longitudinal axis) of the nanofiber. The carbon nanofibers aresometimes referred to herein as “ribbon” nanofibers and multifacetedtubular nanofibers. The carbon nanostructures of the present inventionare distinguished from the so-called “fibrils” or cylindrical carbonnanostructures. The terms “carbon nanofibers” and “carbonnanostructures” are sometimes used interchangeably herein. The graphitesheets that compose the nanostructures of the present invention areeither discontinuous sheets or faceted flat-faced tubular structures. Onthe other hand, cylindrical carbon nanostructures, or “fibrils” arecomposed of continuous circular graphite sheets and can be representedby tube within a tube structure having a substantially hollow center. Inaddition, the carbon nanofibers of the present invention have a uniqueset of properties, that includes: (i) a nitrogen surface area from about40 to 300 m²/g; (ii) an electrical resistivity of 0.4 ohm·cm to 0.1ohm·cm; (iii) a crystallinity from about 95% to 100%; and (iv) a spacingbetween adjacent graphite sheets of 0.335 nm to about 1.1 nm, preferablyfrom about 0.335 nm to about 0.67 nm, and more preferably from about0.335 to about 0.40 nm.

[0020] The catalysts used to prepare the carbon nanofibers of thepresent invention are bulk metals in powder form wherein the metal isselected from the group consisting of iron, iron:copper bimetallics, andiron:nickel bimetallics. It is well established that the ferromagneticmetals, iron, cobalt, and nickel, are active catalysts for the growth ofcarbon nanofibers during decomposition of certain hydrocarbons or carbonmonoxide. Efforts are now being directed at modifying the catalyticbehavior of these metals, with respect to nanofiber growth, byintroducing other metals and non-metals into the system. In thisrespect, copper is an enigma, appearing to be relatively inert towardscarbon deposition during the CO/H₂ reaction. Thus, it is unexpected thatFe or the combination of Cu or Ni with Fe has such a dramatic effect oncarbon nanofiber growth in the CO/H₂ system in the temperature range ofabout 625° C. to about 725° C. Preferably from about 650° C. to about725° C., and more preferably from about 670° C. to about 725° C.Iron:copper catalysts are preferred for preparing the carbonnanostructures of the present invention.

[0021] The average powder particle size of the metal catalyst will rangefrom about 0.25 nanometers to about 5 micrometer, preferably from about1 nanometers to about 3 micrometer and more preferably from about 2.5nanometers to about 1 micrometer. When the catalyst is a bimetalliccatalyst, the ratio of the two metals can be any effective ratio thatwill produce substantially crystalline carbon nanofibers in which thegraphite sheets are substantially parallel to the longitudinal axis ofthe nanofiber, at temperatures from about 625° C. to about 725° C. inthe presence of a mixture of CO/H₂. The ratio of iron to either copperor nickel will typically be from about 1:99 to about 99:1, preferablyfrom about 5:95 to about 95:5, more preferably from about 3:7 to about7:3; and most preferably from about 6:4 to about 7:3. The bimetalliccatalyst can be prepared by any suitable technique. One preferredtechnique is by co-precipitation of aqueous solutions containing solublesalts of the two metals. Preferred salts include the nitrates, sulfates,and chlorides of iron, copper, and nickel particularly the nitrates.

[0022] The resulting precipitates are dried and calcined to convert thesalts to the mixed metal oxides. The calcined metal powders are thenreduced at an effective temperature and for an effective time.

[0023] The catalyst powders used in the present invention are preferablyprepared by the co-precipitation of aqueous solutions containingappropriate amounts of iron, nickel and copper nitrates using ammoniumbicarbonate. The precipitates were dried overnight at about 110° C.before being calcined in air at 400° C. to convert the carbonates intomixed metal oxides. The calcined powders are then reduced in hydrogenfor 20 hours at 400° C. Following this treatment the reduced catalyst iscooled to room temperature in a helium environment before beingpassivated in a 2% oxygen/helium mixture for 1 hour at about roomtemperature (24° C.).

[0024] It is known that carbon nanostructures can be prepared byreacting a catalyst in a heating zone with the vapor of a suitablecarbon-containing compound. While the art teaches a wide variety ofcarbon-containing compounds as being suitable, the inventors hereof havefound that only a mixture of CO and H₂ will yield carbon nanofibers withunexpected high crystallinities in the unique structures of nanofibersof the present invention in the temperature range of about 625° C. toabout 725° C. That is, crystallinities greater than about 95%,preferably greater than 97% more preferably greater than 98%, and mostpreferably substantially 100%.

[0025] After the nanofibers are grown, it may be desirable to treat themwith an aqueous solution of an inorganic acid, such as a mineral acid,to remove any excess catalyst particles. Non-limiting examples ofsuitable mineral acids include sulfuric acid, nitric acid, andhydrochloric acid. Preferred is hydrochloric acid.

[0026] It is within the scope of this invention to increase the spacingbetween the graphite sheets by any suitable means, such as byintercalation. Intercalation involves incorporating an appropriateintercalation compound between platelets. Intercalation compoundssuitable for graphite structures are comprehensively discussed inApplications of Graphite Intercalation Compounds, by M. Inagaki, Journalof Material Research, Vol 4, No.6, November/December 1989, which isincorporated herein by reference. The preferred intercalation compoundsfor use with the nanofibers of the present invention are alkali andalkaline-earth metals. The limit to which the spacing of the graphitesheets will be increased for purposes of the present invention will bethat point wherein the carbon nanofibers no longer can be characterizedas graphitic. That is, the spacing can become so large that the carbonnow has properties different than those of graphite. In most cases theelectro-conductivity is enhanced. It is important for the practice ofthe present invention that the carbon nanofibers maintain the basalplane structure representative of graphite.

[0027] A major advantage of the graphite nanofibers of the presentinvention over other graphitic materials is their flexibility withregard to modification of surface chemistry. For example, the carbonnanostructures of the present invention contain a substantial number ofedge sites, which are also referred to as edge regions. The edge regionsof the nanostructures of the present invention can be made either basic(introduction of NH₄ ⁺groups) or acidic (addition of COOH⁻groups) by useof appropriate methods. Furthermore, the presence of oxygenated groups(hydroxyl, peroxide, ether, keto or aldehyde) that are neither acidicnor basic in nature can impart polarity to the graphite structure. Thesegroups in turn can react with organic compounds to house uniquestructures for separations. Polar groups will promote the interaction ofcarbon edge atoms with other polar groups such as water. As aconsequence, the interaction of graphitic materials with aqueoussolutions can be greatly enhanced due to the presence of acid, basic orneutral functionality.

[0028] The distribution of polar groups in active carbon (non-graphitic)occurs in a random fashion, whereas the graphitic nanofibers of thepresent invention, such sites are located at the edges of the graphenelayers. Addition of oxygenated groups can be achieved by selectedoxidation treatments including treatment with peroxides, nitric acid,potassium permanganate, etc. Functionality can also be incorporated byelectrochemical oxidation, at for example 2.3 volts for various periodsof time. The nature of the groups will be dependent upon the oxidationtime and the voltage. Polar sites can also be eliminated by reduction,out-gassing in vacuum at 1000° C. or treatment in hydrazine at about 35°C. Following this procedure, the graphite nanofiber will becomehydrophobic. Theodoridou and coworkers, (Met. 14, 125 (1986)),demonstrated that very efficient surface oxidation of carbon fibers canbe achieved by d.c. oxidation or repetitive anodic oxidation andcathodic reduction of the material in acidic, alkaline or neutralaqueous media. It was believed that this method had the advantage overother procedures in that thick layers of surface oxides could beproduced without damaging the fiber structure. These workers alsocapitalized on the conductive properties of graphitized carbon fibers tointroduce various noble metals onto such materials via the use ofelectrochemical procedures. The possibility of controlling thefunctionality of the graphite surface could have a direct impact on boththe chemistry of the supported metal particles and their morphologicalcharacteristics.

[0029] The present invention will be illustrated in more detail withreference to the following examples, which should not be construed to belimiting in scope of the present invention.

[0030] Gas flow reactor experiments were carried out in a horizontalquartz tube (40 mm i.d. and 90 cm long) contained in a Lindberg tubefurnace, at temperatures over the range of about 450° C. to 700° C. Gasflow rates to the reactor were regulated by MKS mass flow controllers.In a typical experiment, 50 mg of given catalyst powder was dispersed ina substantially uniform manner along the base of a ceramic boat, whichwas subsequently placed at the center of the reactor tube. Afterreduction of the sample at 600° C. for 2 hours, the system was flushedwith helium and brought to the desired temperature level before beingreacted with in the CO/H₂ mixture for a period of 2 hours. The totalamount of solid carbon formed in any given experiment was determined atthe completion of the reaction by weight difference. The composition ofthe gas phase was measured at regular intervals by taking samples of theinlet and outlet streams, which were then analyzed by gas chromatographyusing a 30m megabore (CS-Q) capillary column in a Varian 3400 GC unit.Carbon and hydrogen atom balances, in combination with the relativeconcentrations of the respective components, were applied to obtain thevarious product yields. In order to obtain reproducible carbondeposition data it was necessary to follow an identical protocol foreach experiment.

[0031] The structural details of the carbon materials resulting from theinteraction of the CO/H₂ mixtures with the various powdered bimetalliccatalysts were examined in a JEOL 2000 EX II transmission electronmicroscope that was fitted with a high resolution pole piece capable ofproviding a lattice resolution of 0.18 nm. Temperature programmedoxidation studies (TPO) of the various carbon materials were carried outin a Cahn 2000 microbalance in the presence of a CO₂/Ar (1:1) mixture ata heating rate of 5°/min. The degree of crystallization of a given typeof carbon nanostructure was determined from a comparison of theoxidation profile of two standard materials, amorphous carbon and singlecrystal graphite when treated under the same conditions.

Example 1

[0032] In the first set of experiments selected Fe:Cu catalysts wereheated in the presence of a CO/H₂ (4:1) mixture at temperatures rangingfrom 450° C. to 700° C. Table I below shows the number of grams ofcarbon nanofibers per weight of catalyst produced after a period of 2hours at each temperature. In each case the optimum yield of carbonnanofibers was generated at temperatures between 550° C. and 600° C. Themost active catalysts were those that contained a larger fraction ofiron than copper. TABLE I Effect of Temperature on the amount of CarbonNanofibers (grams/grams of Catalyst) from the Decomposition of CO/H₂over selected Fe:Cu Powders Temperature (° C.) Fe:Cu (1:9) Fe:Cu (3:7)Fe:Cu (7:3) 450 1.10 1.15 1.31 500 2.55 4.15 10.83 525 4.48 550 6.149.81 12.02 600 7.86 10.15 11.55 625 5.07 650 3.72 4.21 4.40 700 1.241.15 1.31

Example 2

[0033] A second series of experiments was carried out at 550° C. underconditions where selected Fe:Cu catalysts were heated in CO/H₂ mixturesin which the percent of H₂ was progressively increased. The datapresented in Table II below shows that the number of grams of carbonnanofibers per weight of catalyst produced after 2.5 hours reached amaximum for each system when the reactant gas contained between 20 to50% of hydrogen. TABLE II Effect of Percent H₂ in the CO/H₂ reactantmixture on the amount of Carbon Nanofibers (grams/grams of Catalyst)formed over Fe:Cu Catalysts at 550° C. Catalyst 20% H₂ 50% H₂ 80% H₂Pure Fe 17.53 16.86 14.16 Fe—Cu (7:3) 16.63 17.23 12.96 Fe—Cu (5:5)16.41 15.74 12.14 Fe—Cu (3:7) 13.78 13.71 12.51 Fe—Cu (1:9) 8.7 10.4110.79

Example 3

[0034] Another set of experiments was performed at 600° C. underconditions where selected Fe:Cu catalysts were heated in CO/H₂ mixturesin which the percent of H₂ was progressively increased. The datapresented in Table III below shows that in this case the number of gramsof carbon nanofibers per weight of catalyst produced after 2.5 hoursreached a maximum for each system when the reactant gas contained 20% ofhydrogen. TABLE III Effect of Percent H₂ in the CO/H₂ reactant mixtureon the amount of Carbon Nanofibers (grams/grams of Catalyst) formed overFe:Cu Catalysts at 600° C. Catalyst 20% H₂ 33% H₂ 50% H₂ 67% H₂ 80% H₂Fe—Cu (1:9)  7.86 7.37 7.11 5.26 3.96 Fe—Cu (3:7) 10.15 8.91 7.44 6.354.05 Fe—Cu (7:3) 11.85 9.33 8.99 4.77 3.23

Example 4

[0035] In a set of experiments carried out at 600° C. for 2 hours it wasfound that the number of grams of carbon nanofibers per weight ofcatalyst produced after 2.5 hours with a CO/H₂ mixture was dependentupon the percentage of copper in the Fe:Cu bimetallic catalyst. It canbe seen from Table IV below that as the fraction of copper exceeds 40%there is a gradual decrease in carbon nanofiber yield. It can also beseen that a catalyst containing pure copper does not produce carbonnanofibers. TABLE IV The effect of catalyst composition on carbonnanofiber formation from the Fe—Cu catalyzed decomposition of CO/H₂(4:1) after 1.0 hours at 600° C. % Copper in catalyst Grams of carbonnanofibers/grams catalyst 0 8.8 30 11.65 50 11.60 70 10.25 80 9.10 907.35 95 4.70 100 0

Example 5

[0036] In a further set of experiments the overall degree ofcrystallinity of the carbon nanofibers produced from the interaction ofselected Fe:Cu catalysts with a CO/H₂ (4:1) mixture at 600° C. for 2.0hours was determined from temperature programmed oxidation of thenanofibers in CO₂. The characteristics of the controlled gasification ofcarbonaceous solids in CO₂ provides a sensitive method of determiningthe structural perfection of such materials. The data shown in Table Vbelow indicates that the degree of crystallinity of carbon nanofibersgenerated from an Fe—Cu (7:3) catalyst is significantly higher than thatof the same type of nanofibers grown under identical reaction conditionson a pure iron catalyst. TABLE V Percent reactivity of carbon nanofibersin CO₂ as a function of reaction temperatures Carbon Material 805° C.900° C. 950° C. 1000° C. 1050° C. Nanofibers from Fe 29.1% 52.0% 72.8%86.2% 100.0% Nanofibers from  5.2% 12.8% 30.6% 57.0% 100.0% Fe—Cu (7:3)

Example 6

[0037] In a series of characterization studies performed in a highresolution transmission electron microscope, small sections of carbonnanofibers grown from the decomposition of CO/H₂ mixtures at 600° C.over various metal and bimetallic catalyst systems were examined andrepresentative micrographs taken of each sample. A compilation of theobservations made from inspection of several micrographs from eachsample is given in Table VI below. Also included for comparison purposesare corresponding data for nanofibers grown from the interaction of thesame series of catalysts with C₂H₄/H₂ at 600° C. TABLE VI Comparison ofstructural features of carbon nanofibers from the decomposition of CO/H₂(4:1) and C₂H₄/H₂ (4:1) over various metal and bimetallic catalysts at600° C. Nanofiber Structure Catalyst C₂H₄/H₂ CO/H₂ Fe No nanofibergrowth Platelet Ni Straight amorphous No nanofiber growth nanofibers CoStraight amorphous No nanofiber growth nanofibers Fe—Ni Straight coiled& branched Faceted Tubular/Ribbon “herring-bone” Ni—Cu Straight coiled &branched No nanofiber growth “herring-bone” Co-Cu Amorphous straight, Nonanofiber growth Coiled & branched Fe—Cu Straight coiled & branchedPlatelet “herring-bone”

[0038] A carbon nanofiber having graphite sheets at an angle to thelongitudinal axis of the nanofiber is referred to as a “herringbonestructure”.

Example 7

[0039] In another series of characterization studies, performed in ahigh resolution transmission electron microscope, samples of carbonnanofibers grown from the decomposition of CO/H₂ mixtures over apowdered iron catalyst at temperatures over the range 550 to 670° C.were examined. The data presented in Table VII below indicates thatthere is a very narrow temperature window, 600 to 625° C., where thestructures of the nanofibers are produced exclusively in the form ofplatelet structures. Below this temperature the solid carbon product isfound to consist of a mixture of herring-bone and plateletconformations, whereas at temperatures of 650° C. there is a tendencyfor the structures to acquire a faceted tubular or ribbon arrangement,which becomes the only form at 670° C. TABLE VII Characteristics ofcarbon nanofibers produced from the iron catalyzed decomposition of aCO/H₂ (4:1) mixture as a function of reaction temperature CatalystTemperature (° C.) Nanofiber Structure Fe 550 Herring-bone & Platelet Fe580 Herring-bone & Platelet Fe 600 Platelet Fe 625 Platelet Fe 650Platelet & Faceted Tubular/Ribbon Fe 670 Faceted Tubular/Ribbon

Example 8

[0040] In another series of characterization studies, performed in ahigh resolution transmission electron microscope, samples of carbonnanofibers grown from the decomposition of CO/H₂ mixtures over apowdered iron-copper (7:3) catalyst at temperatures over the range 550to 670° C. were examined. The observations from these experiments arepresented in Table VIII below. TABLE VIII Characteristics of carbonnanofibers produced from the iron-copper (7:3) catalyzed decompositionof a CO/H₂ (4:1) mixture as a function of reaction temperature CatalystTemperature (° C.) Nanofiber Structure Fe—Cu (7:3) 550 Herring-bone &Platelet Fe—Cu (7:3) 575 Platelet Fe—Cu (7:3) 600 Platelet Fe—Cu (7:3)625 Platelet Fe—Cu (7:3) 650 Platelet & Faceted Tubular/Ribbon Fe—Cu(7:3) 670 Faceted Tubular

What is claimed is:
 1. A substantially crystalline graphitic carbonnanofiber comprised of substantially graphite sheets that aresubstantially parallel to the longitudinal axis of the nanofibers,wherein the distance between graphite sheets is from about 0.335 nm toabout 0.67 nm, and having a crystallinity greater than about 95%.
 2. Thenanofiber of claim 1 wherein said substantially graphite sheets areseparate and non-continuous sheets.
 3. The nanofiber of claim 1 which ischaracterized as having continuous substantially graphite sheets forminga non-cylindrical multifaceted tubular structure.
 4. The nanofiber ofthe claim 1 wherein the distance between the graphite sheets is fromabout 0.335 and 0.40 nm.
 5. The nanofiber of claim 1 wherein at least aportion of the edge regions of the nanofiber contain a functional groupselected from the group consisting of basic groups, acidic groups, andoxygenated groups.
 6. The nanofiber of claim 5 wherein the functionalgroup is a basic group that is a NH₄+ group.
 7. The nanofiber of claim 5wherein the functional group is an acid group which is a COOH⁻ group. 8.The nanofiber of claim 5 wherein the functional group is an oxygenatedgroup selected from the group consisting of hydroxyl, peroxide, ether,keto, and aldehyde.
 9. A substantially crystalline graphitic carbonnanofiber comprised of substantially graphite discontinuous sheets thatare substantially parallel to the longitudinal axis of the nanofibers,wherein the distance between graphite sheets is from about 0.335 nm toabout 0.67 nm, and having a crystallinity greater than about 95%. 10.The nanofiber of the claim 9 wherein the distance between the graphitesheets is from about 0.335 and 0.40 nm.
 11. The nanofiber of claim 9wherein at least a portion of the edge regions of the nanofiber containa functional group selected from the group consisting of basic groups,acidic groups, and oxygenated groups.
 12. The nanofiber of claim 11wherein the functional group is a basic group that is a NH₄+ group. 13.The nanofiber of claim 11 wherein the functional group is an acid groupwhich is a COOH⁻ group.
 14. The nanofiber of claim 11 wherein thefunctional group is an oxygenated group selected from the groupconsisting of hydroxyl, peroxide, ether, keto, and aldehyde.
 15. Asubstantially crystalline graphitic carbon nanofiber comprised ofcontinuous substantially graphite sheets that are substantially parallelto the longitudinal axis of the nanofibers and which has a substantiallynon-cylindrical multifaceted tubular structure, wherein the distancebetween graphite sheets is from about 0.335 nm to about 0.67 nm, andhaving a crystallinity greater than about 95%.
 16. The nanofiber of theclaim 15 wherein the distance between the graphite sheets is from about0.335 and 0.40 nm.
 17. The nanofiber of claim 15 wherein at least aportion of the edge regions of the nanofiber contain a functional groupselected from the group consisting of basic groups, acidic groups, andoxygenated groups.
 18. The nanofiber of claim 17 wherein the functionalgroup is a basic group that is a NH₄+ group.
 19. The nanofiber of claim17 wherein the functional group is an acid group which is a COOH group.20. The nanofiber of claim 17 wherein the functional group is anoxygenated group selected from the group consisting of hydroxyl,peroxide, ether, keto, and aldehyde.
 21. A process for producing asubstantially crystalline graphitic nanofiber wherein at least a portionof which are comprised of graphite sheets that are substantiallyparallel to the longitudinal axis of the nanofiber, which processcomprises reacting a mixture of CO/H₂ in the presence of a catalystselected from the group consisting of Fe, Fe:Cu bimetallic, and Fe:Nibimetallic powder catalysts for an effective amount of time at atemperature from about 625° C. to about 725° C.
 22. The process of claim21 wherein said nanofibers are characterized as having separate andnon-continuous substantially graphite sheets.
 23. The process of claim21 wherein said nanofibers are characterized as having continuoussubstantially graphite sheets forming a non-cylindrical multifacetedtubular structure.
 24. The process of claim 21 wherein the catalyst isan Fe:Cu bimetallic wherein the ratio of Fe to Cu is from about 1:99 toabout 99:1.
 25. The process of claim 24 wherein the ratio of Fe to Cu isfrom about 3:7 to about 7:3
 26. The process of claim 21 wherein thecatalyst is an Fe:Ni bimetallic wherein the ratio of Fe to Ni is fromabout 1:99 to about 99:1.
 27. The process of claim 26 wherein the ratioof Fe to Ni is from about 3:7 to about 7:3
 28. The process of claim 21wherein the ratio of CO to H₂ is from about 95:5 to about 5:95.
 29. Theprocess of claim 28 wherein the ratio of CO to H₂ is from about 80:20 toabout 20:80.
 30. The process of claim 25 wherein the ratio of CO to H₂is from about 80:20 to about 20:80.
 31. The process of claim 21 whereinthe crystallinity of the nanofiber is greater than about 98%.
 32. Theprocess of claim 25 wherein the crystallinity of the nanofiber isgreater than about 98%.
 33. The process of claim 21 wherein the particlesize of the bimetallic powder is from about 0.25 nanometer to about 5micrometer.
 34. The process of claim 33 wherein the particle size of thebimetallic powder is from about 2.5 nanometers to about 1 micrometer.